Polishing machine



Nov. 2, 1948. H. T. NICHOLAS 2,452,863

POLISHING MACHINE Filed sept. 29, 1945' 5 sheets-sheet 1 INVENTOR. E@ iHf/PrT/V/cnoms H #menen N0 2 1948. H. T. NlcHoLs 2,452,863

POLI-SHING MACHINE Filed sept. 29, 1945 5 sheets-sheet 2 N0v.` 2,1948 H.T. NICHOLAS 2,452,863

PoLIsHING MACHINE Filed Sept. 29, 1945 5 Sheets-Sheet 5 @da di@ Error/nm1\1mf.2,`1948. H. T. NICHOLAS 2,452,863

POLIISHING MACHINE Filed sept. 29,. 1945 5 sheets-sheet 4 By Y @22204,vlwf 17T/BIENE Y! FIG. 7

Nov. 2, 1948.

Filled sept. 29, 1945 H. T. NICHOLAS POLISHING MACHINE 5 Sheets-Sheet 5l INVENTOR. #Emst/ri- TAI/mams liz-roem: y1

Patented Nov. 2, 194.8

POLISHING MACHINE Herbert T. Nicholas, Huron, Ohio, assigner to NicholasEquipment Company, a partnership Application September 29, 1945, SerialNo. 619,367

11 Claims.

This invention relates to an improved polishing or abrading machine, andespecially to an improved machine which will be particularly welladapted for polishing knife blades or similar articles. These,therefore, are the general ob jects of the present invention.

A more specic object of the invention is the provision of an improvedactuating mechanism for passing workpieces between a pair of coactingpolishing or abrading rolls, as well as the provision of an improvedmechanism for controlling the number of passes to be made by theworkpieces.

Another object of this invention is to provide a mechanism for polishingor abrading work pieces, between a pair of coacting polishing orabrading rolls, including a method of control for the peripheral speedof the rolls, regardless of variations between the rolls caused by wearand the like.

A further object of the invention is to provide an improved polishing orabrading machine, of the type using a pair of coacting rolls betweenwhich the work is passed, the mechanism of which will be so arranged asto eliminate, for practical purposes, undesired vibrations andchattering, either of which is apt to blemish the work pieces, as wellas result in early deterioration of the mechanism.

Other objects and advantages of this invention;

will become more apparent from the following specification, referencebeing had to an embodiment of the invention illustrated in theaccompanying drawings. The essential features of the invention will besummarized in the claims.

In the drawings, Fig. 1 is a front elevation of an abrading or polishingmachine constructed in accord with the present invention; Fig. 2 is anend elevation of the machine, certain parts being broken away to moreclearly illustrate the inn ternal construction; Fig. 3 is a horizontalsection through the machine, the plane of the section being illustratedby the offset lines 3-3 of Fig. 1; Fig. 4 is a sectional detail of aportion of the mechanism used to control the position of the abradingrolls, the plane of the section being indicated by the lines 4-4 of Fig.1; Fig. 5 is a diagram of the mechanism used to pass the workpiecesbetween the polishing or abrading rolls, and Fig. 6 is a diagram ofelectrical circuits used to control the operation of the roll drivingmotors.

In general, the machine illustrated in the drawings comprises asubstantially rectangular frame-like structure ID, provided with a tableII. A pair of polishing rolls I2 and I4 are supported with their axesparallel with each other in a horizontal plane beneath the table II andwithin the frame structure III. These rolls are driven at a relativelyhigh rate of speed prefer- 2 ably by respective combined motor and speedreduction units I and I6 which are mounted on the table II. These unitsare of a type to facilitate a comparatively iine and individual adjust-5 ment of the peripheral speed of their respective rolls.

Workpieces A, supported by a workholder I'I, are reciprocated up anddown between the rolls by a hydraulically actuated mechanism mountedwithin a hollow column I8 which rises vertically from substantially thecenter of the table II. A mechanism driven by a motor IIl atop the tableII imparts a substantially horizontal movement to the workpieces as theypass between the rolls I2 and I4. The speed of travel of the workpiecesis controlled by a pair of settable knobs and 2| which are carried by aninstrument panel 22 at the front of the machine, while the number ofpasses the workpieces are to make is controlled by a manually operableknob 23 also positioned on the instrument panel.

A feature of the present invention is the method of and mechanism forcontrolling the peripheral speed of the abrading rolls I2 and I4. A pairof ammeters 24 and 25 are mounted on the instrument panel and are soconnected in the electrical circuit of the machine that the operator mayaccurately determine when the peripheral speed of the abrading rolls hasbeen equalized. I have found that the peripheral speed is synchronizedwhen the current flowing through each motor is identical. Suitablehandwheels 26 and 21 mounted on respective speed-reduction units |15 andI6 permit manual adjustment of the peripheral speed of their respectiverolls.

The frame I0 comprises, as shown in Figs. 1 and 2, a rectangular base 30having corner posts 3| in the form of angle irons. These posts supportthe table structure II. Suitable cross braces, some of which are shownin Fig. 2, at 32, serve to give rigidity to the frame structure. Thetable II has a downwardly extending skirt 33 from which pivoted hangers34 depend. The rolls I2 and I4 are each mounted between the lower endsof these hangers.

The rolls illustrated are polishing rolls. These rolls are indicated asbeing built up of a series of fabric discs which are assembled on shafts35 and which are held thereon by clamping discs 36 and nuts 31. Thefabric discs are yieldable and generally have their peripheriesimpregnated with a polishing rouge, emery or the like, dependent uponthe type of polishing or abrading operation to be performed.

The rolls I2 and I4 are journalled in the lower ends of the hangers 34with their axes parallel with each other in substantially the samehorizontal plane, and with their bite at the transverse center of theframe. As shown, the ends of each roll shaft are mounted inself-aligning bearlare embraced by threaded sleeves @-5.

facing sleeves lid.

'ducer unit.

ings 38 which in turn are adjustably positioned in the lower ends oftheir respective hangers @il by screws 3S). Suitable collars lillprevent axial displacement of the shafts in their bearings.

The upp-er ends of the roll supporting hangers 3d are pivoted as at dito the table l l and are swingable about their pivots to enable therolls to be moved toward and from each other and thereby adjust theirbite. The movement of the hangers is controlled by hand wheels Il?(Figs. l and 4). Each hanger is provided with a threaded rod 43. Theserods are pvo-ted as at ed to the respective hangers and extend outwardlytherefrom toward the sides of the frame l il where they rhe sleeves 45for respective rolls are journalled in respective beams 46 (Figs. 3 andLl) the ends of which are pivoted as at 4l in the frame posts 3l. Handwheels 42 are secured to the forwardly facing sleeves d5 which areconnected by gears i8 and drive chains 49, with the respectiverearwardly Each sleeve l5 is prevented from axial movement by an arm '59carried by a beam i6 and arranged to coact with a slot 5i) in itssleeve. Accordingly, if either hand wheel di! is rotated, its respectiveroll l2 or ifi will be moved toward or from the other roll, the axes ofthe rolls remaining parallel-at all times. This provides an accurateadjustment of the pressure lbetween the rolls as well as providing foraccurate alignment of the roll bite with the workpieces.

The combined motor and speed reduction units I5 and I6 are bestillustrated in Fig. 3. These units are substantially identical, eachcomprising an electric motor 5i, the armature shaft 52 of which extendsinto a housing 53 of a speed re- Secured to the shaft 52 is a conY tothe hub t5 of which a cooperating cone spIined. The cone 56 is moved toand from the cone 5t by a nut 5l which is restrained from rotation bythe housing and which has a lug 5 engagement with a peripheral groove 5@'in the hub of the cone. The nut is moved axially by a threaded shaftfill to which one of the hand wheels 26.or 2l is secured.

A V shaped belt El connects the variable pitch .cones 5S, d with asimilar pair of vcones 52, (it,

which actuate the driven shaft tlof the speed reducer unit. The cone 62is splined to shaft iid and has an elongated hub 65 to which the cone G3is splined. A compression spring 5t is interposed between the cone 63and a collar el on the hub of the cone S2 and serves to move the cones62, 63 toward each other to eliminate the slack in the belt 6l. Theconstruction is such that as the cones lid, 55 are separated, the conesiii, approach each other, thus varying the relative speeds of the shafts52 and 5d in the usual manner. The speed reducer shafts t4 are eachprovided with sheaves G8 which are drivingly connected with sheaves (Se0n their respective roll shafts 35 by driving belts lli, as indicated inFig.

The workholder il is best illustrated in Figs. l and 2 and as thereshown it comprises a plate 'il to which the workpieces A are clamped insuitable manner. The upper end of the plate li is secured to a T rail l2which is mounted between ya pair of inverted T rails 'i3 carried by acarriage 74. Preferably, the arrangement is such that the workholder maybe slid into position on the carN riage. The carriage is pivotallyconnected by a pair of parallel links 'il and i8 to outwardly eX-tending arms 'l5 of a sleeve lb, which is slidably mountedon the columnI8.

The'sleeve 16 is reciprocated on the column i8 by a hydraulicallyoperated mechanism t0 thereby pass the work W vertically between therolls l2 and ifi. Mounted in the frame it (Figs. 2 and 5) is an oilstorage tankiiii from which oil is drawn through a conduit 8i by apressure pump B2. rihis pump is actuated by an electric motor 83. Thefluid passes from the pump 82 through a conduit Sd to a reversing valve85. In the position of the valve 8.5 shown in Fig. 5, the fluid underpressure passes from the valve through a conduit 85, a, regulating valveSi, and a conduit 38 to the lower end of a cylinder ed, thus raising thepiston 9B thereof. The cylinder dii is positioned within and is securedto the column le, while the upper end of the piston rod @i thereof issecured to a bar SE (Fig. 2) by nuts 93. This bar extends outwardly'from the column i@ through slots 9d therein and its outer ends aresecured tothe sleeve it.

While the piston and Wcrkholder move upwardly, fluid is discharged fromthe upper portion of the cylinder 239 through a conduit S5, a regulatingvalve tifa, and a conduit ill to the reversing valve t5, from which thefluid returns through a discharge or exhaust conduit 93 to the storagetanlr 3d. The reversing of the control member or piston QQ of thereversing valve 65 causes the reversal of the direction of fluidflo-wabove escriben'. between the reversing valve- 35 and the cylinder B91and accordingly lowers the sleeve and ivorkholder il.

As heretofore mentioned, the workpieces are horizontally while they passbetween the rolls i2 and lll. The mechanism for accomplishn ing this is-best shown in 3. A motor lili? is mounted on the table ii and isprovided'with a speed reducer unit indicated at lili. The driven iil ofthe unit lili is provided with an eccentric pin M32 which is connectedby a link d3 with a slide itil. This slide is mounted in a guidewaycarried by the table Il l and embraces the parallel linlr li heretoforedescribed as connecting the sleeve "it with the workholder il. Thisrotation of the shaft it@ causesthe workholder to be reciprocatedaxialiyof the polishing rolls. The amount of this axial movement is small andits frequency great in comparison with the vertical movement. Thus aneven polishing action is accomplished.

The frequency of the horizontal travel of the Worlrhclder is determinedby the rate of speed'of the speed reducer shaft l The rate of speed andaccordingly the frequency of the vertical movement is determined b f theregulating valves 3l and 95. These valves are identical in constructionand are diagrammatically illustrated in Fluid under pressure iiovvs fromthe reversing valve Sii into one of these valves, it enters. the lowerchamber lill of the valve and forces a valve member from its seatagainst the action of spring i te. 'Thereupon the fluid passes,substantially without restriction, into the upper chamber i it of thevalve and thence to one end of the cylinder 23E. However, thedischarging fluid from the other end of the cylinder t9 passes directlyinto the upper chamberl i it of the other regulating valve at. The valvemember i t8 of this valve is closed due to the action of its spring illsand the absence of pressure in its lower chamber, accordingly thisreturning iluid must pass through a restricted orifice ill in the wallbetween the upper and lower chambers. The effective areaof the orificelli is regulated by an adjustable needle valve l i2 to which the respective speed control knob. 2t' or vEiis secured.

l.The controllingofthe rate of-travel of the workholder by controllingthe flo-w of fluid from the cylinder 80 provides an accurate regulationof the rate of travel and is independent of pulsating eiects of thepump. Likewise, as pressure is maintained at both ends of the piston,the movement of the workholder is steady and even, thus enhancing thepolishing operation. The elimination of gear or cam driven mechanism forpassing the work between the polishing rollsassists materially inreducing vibration and chattering of the workpieces. The use of ahydraulic drive system permits infinite variations in the rate of travelof the workpieces and permits adjustments to be made for the purpose ofeliminating vibratory eiects which are ordinarily present in machines ofthis general type.

The length of vertical stroke imparted to the workholder is controlledby a pilot valve |I4. This valve in turn controls the reversing valve 85and Ais best illustrated in Fig. 5. The pilot valve may comprise acylinder provided with ports |,I and I I6 which are connected toopposite ends of the reversing valve 85 by conduits and IIB. rThe pilotvalve is also provided with two other ports IIS and |20 which areconnected by conduits |2| and |22 with the pressure line 84 and exhaustline 98 of the hydraulic system as heretofore described. The pilot valveis provided with a vane I-23 which divides the valve into two chambers.The position of the vane |23 is controlled by a pair of cams |24 whichare adjustably mounted on a bar .|25 carried by an arm 'I5 of thereciprocating sleeve 16 heretofore described and which is connected withthe piston rod 9|. These cams are arranged to engage and swing a lever|26 which is connected :by a link |21 with an arm |28 of the vane.

The arrangement of the pilot valve mechanism is such that, when theparts are in the position shown in Fig. 5 (with the piston movingupward), the conduits IIB and |2| are in communication with each other,as are the conduits I|'I and |22. Thus fluid pressure is applied to movethe reversing valve control member 95 to the left (Fig. 5). When,however, the lower cam |24 strikes the lever |26 the vane will rotate,bringing the conduit II'I into communication with the conduit |2| andbringing the conduit |I8 into communication with the conduit |22. Thiswill cause the control member 99 of the reversing valve 85 to move tothe right (Fig. 5) and reverse the direction of ilow of uid to and fromthe cylinder 89. n The number of passes that the workpieces make betweenthe polishing rolls I2 and I4, is controlled by a valve |30 which isadjusted by the manually operable knob 23 heretofore mentioned as beingmounted on the instrument ypanel 22. This valve is best illustrateddiagrammatically in Fig. 5 and as there shown comprises a cylinder |3Ihaving an inlet port |32 connected by a conduit |33 with the pressureline 84, and an exhaust port |34 which is connected by a conduit |35with the exhaust conduit 98. A valve member in the form of a plug |36,having a peripheral groove |31 is rotatably mounted within the valvecylinder. a ratchet |38 and pivotally mounted about the axis of the plugis a lever |39 carrying a springpressed ratchet pawl |40, the ratchetpawl is moved in a step-by-step movement by the cams |24. As the lowercam |24 rises in response to the rising movement of the piston 90, itengages a lever |4I which is connected .by a link |42 with the lever arm|39 which carries the ratchet p'awlA |40.v

Secured to this plug is The arrangement of the ratchet advancingmechanism is such that the ratchet is advanced one tooth at the end ofthe upward stroke of the piston. A spring |43 acting on ,the lever |4|returns the ratchet pawl and the associated linkage to their normalpositions. The usual detent pawl (not shown) is provided to maintain theratchet wheel |38 in its advanced position. The gap or groove |3I in theplug |36 is arranged to bring the ports |32 and |34 of the valvestructure in communication with each other, thus bringing the pressureline 84 into direct communication with the exhaust line 98, whereuponthe movementfof the piston will cease due to a loss of pressure in theoperating system heretofore described. Thus the number of passes of thewheel and work pieces is controlled by the angular position of a plug|36 of the valve |30.

When the Workpieces are first inserted in the machine the operatorgrasps the knob 23 and moves it in a counterclockwise direction to adistance equal to that occupied by the number of ratchet teethequivalent to the number of passes desired. For convenience, theinstrument panel is provided with -a dial 23 A to enable the operator tomanually move the plug to its starting position.

As heretofore described, synchronization of the peripheral speed of therolls I2 and I4 is manually controlled by the actuation of thehandwheels 26 and 2'| which regulate the speed of the driven shafts oftheir respective speed reducer units. I have found that by placing anamineter in the motor circuit of each of the roll driving motors, and byusing substantially identical motors, the amperage reading indicated byeach of these members is the same when the rolls are in synchronization.Thus, the operator may manipulate the handwheels 26 and 2l until thereading on the ammeters are identical, whereupon the peripheral speed ofthe rolls will be synchronized, thereby preventing undue abrasive wearon the rolls and eliminating the overloading of leither motor.

The peripheral or surface speeds of the rolls I2 and I4 are synchronizedwhile the driving motors are under load conditions, i. e., while therolls are in working or peripheral contact with each other or the work.Under such conditions the load on the motors, which are identical, willbe identical when the surface speeds of the rolls are identical. This isparticularly true where the rolls are driven at relatively high speedsas is common in polishing machines. This manner of adjusting the surfaceor peripheral speeds of the rolls compensates for variations in thediameter of the rolls due to wear or the like.

The arrangement of the meters and the electrical circuit of the motorsis best illustrated in the electrical diagram of Fig. 6. In this diagramthe motor I5 is shown as being controlled by a relay |50, while themotor I6 is controlled by a relay I5I. Both of these relays include amaster switch mechanism |52, provided with contacts orswitch members|53, |54 and |55, which are arranged, when closed, to connect theirrespective motors with power lines |56, I5'I and |58. One of the switchmembers of each of the relays |50 and I5I, namely, the switch member|54, is connected with a line |59 which leadsto a transformer unit |60of its respective ammeter 25, 24. The meters in turn are connected bylines |6I with the motors, thus placing the meters in series with theirrespective motors so that at all 7 times they indicate the operatingcondition of theirrespective motors.

rThe switch members E52 of the relays ld and l! are normally held in anopen position by respective springs l and are closed by solenoids |53and lill respective, These solenoids, in turn, are controlled by astarter relay lill. Whe-n the apparatus lis rst placed in use, theoperator depresses a starting switch M5 which completes a circuit fromthe power line 55% through a normally close'` stop switch it@ and anormally closed testing switch it? to the line M53, thus energizing asolenoid i653 and moving the switch arm llt* of the starter relay lillagainst the action of its spring lll, thus closing the switch contact ofits relay.

As soon as the relay lill is energized, the starter switch may bereleased, whereupon the solenoid |65) will remain energized through aline il@ which bypasses the starter relay itl' and leads to a switchContact llll and thence to the solenoid HSS), Simultaneously with the`closing of the switch arm llt, a switch contact l5 or the starter relaycompletes a circuit between the power line |55 and the solenoids @63 andits, thus closing the relays 65o and iti. The switch contact |75 isconnected to the power line E55 at a point between the stop switch ttand the testing switch 59'. by a line llt and is connected by a line lllwith the solenoids' M33 and itil, and they in turn are connected to thepower line 358 by lines Il'Si. Thus both relays li and Edt are energizedt ereby starting the operation of the roll mechanism.

To protect the ammeters 2li and 25, under the abnormally high startingload, the starting relay |87 is provided with a pair of switch members|80 and 53E which are connected by lines lili. and E33 respectivelyacross the lines its and l5! of their respective amineters, thusproviding a shunt for the starting c ent and relieving the ammeters ofthe heavy starting load.

After the roll driving motor units it and lli reach their normal drivingoperating speed, the operator depresses the button of the test switch|81, thereby opening the circuit to the line i173 and releasing thesolenoid lila and opening and starting relay i8?. This places theammeters in the circuit of the motors l5 and iii, which are held inoperation by a switch member ist of the relay IEEE. This switch memberis connected by a line E85 with the power line and by a line 86 with thesolenoids ltd and iti, thereby holding both relays |58 and la'l closeddespite the opening of the switch lill. This placing of the ammetersdirectly in the series with their respective motors provides a visibleindication to the operator to enable him to adjust the speed reducerunit to synchronize the peripheral speed of the rollers 2 and ifi.

When it is desired to stop the machine, it is only necessary to depressthe stop switch E65, thus opening the power circuit ld, whereupon therelays iEll and |'.i| will both be released, permitting their springs toreturn them to an open position. A pressure switch is likewise providedto stop the opera-tion of motor lill) should the fluid pressure drivingthe reciprocating mechanism at any time fail. This switch mechanism isbest shown in Fig. 5 and comprises a pressure cylinder is@ which is inseries with the pressure line 84 and is provided with a piston i9 l.|-Ehe arrangement is such that should at any tin e the pressure in theline 84 drop below a predetermined amount, the spring indicated at E92will open a switch |95 which is in series with the. power line |55leading to the d stop switch as shown .in electrical diagram in Fig. 6.l

An important advantage of the present invention is the 'ia-ct that lhave provided a method for indicating the relative peripheral speeds ofthe polishing rolls, and for quickly adjusting the speeds to maintainsynchronization, regardless of the relative sizes of the rolls. Thus,the wear on rolls is materially reduced and the degree of pressuredesired on the work is readily controlled.

claim:

i. A polishing apparatus comprising a polishing roll, a work holdermechanism, means for recurrently moving the work-holder toward and fromthe polishing roll to move a workpiece across the face of the roll, ailuid pressure system for actuating said mechanism, a control valve insaid system, said valve being movable to release lthe :fluid pressure tothereby interrupt the operation thv echanism, means operable during themovein nt of said mechanism for intermittently advancing said controlvalve toward the releasing r sition, and means for adjusting thedistance oi ovemcnt for control valve to become operative whereby thenumber of passes or" the work across the face of the roll may becontrolled.

2. ./l polishing apparatus comprising a pair of polishing rolls, aworkholder mechanism for refrently moving the workholder toward and fromthe bite of the polishing rolls to move a workpiece through the bite ofsaid rolls, a fluid pressure system for actuating said mechanism, acontrol valve in said system, said valve being movable to release theiiuid pressure thereby to interrupt the operation of said mechanism,means operable during the movement of said mechanism ior inittentlyadvancing the control valve tothe releasing position, and means forcontrolling the iiow of iluid in the system, whereby the rate oimovement of the workpiecebetween the bite of the polishing rolls may becontrolled.

A polishing apparatus comprising a polishroll, a workholder mechanismfor recurrently reciprocating the workholder toward and from the roll tomove a workpiece across the face of roll, a uid pressure system foractuating said mechanism, said system including a hydraulic cylinder,piston in said cylinder and connected to actuate said mechanism, asource of uid pressure, a valve in said system to alternately connectend of said cylinder with the source of fluid pressure and to exhaustthe opposite end thereof,

controlled by the movement of said mechanism for actuating said valve,independent valves in said system for adjustably controlling the of flowof the exhausting iluid from each end. ci `said cylinder to therebyindependently control the rate of movement of the workholder in each oiits reciprocating directions, and a pressure release valve in suchsystem operable conseq ent upon a predetermined number of reciprocaticnsof said mechanism to release the pressure supply said system.

fi. il polishing apparatus comprising a pair of oacting polishing rolls,a workholder mechanism or recurrently moving the workholdertoward .nd fr.m the bite oi the polishing rolls to move a wor! ece across thecoacting faces of the rolls, a duid pressure system for actuating saidmechanii i, a control valve in said system, said valve being movable torelease the nuid pressure to the interrupt the operation of themechanism, ratchet means operable by said mechanism for intermittentlyadvancing said control valve toward the releasing position, and meansfor adjusting the distance of movement for said ratchet to becomeoperative to move the rvalve to a releasing position, whereby the numberof passes of the work across the face of the roll may be controlled.

5. A polis-hing apparatus comprising a pair of coacting polishing rolls,a workholder mechanism for recurrently reciprocating the workholdertoward and. from the bite of said rolls to move a workpiece across thecoacting faces of the rolls, a fluid pressure system actuating saidmechanism, including a hydraulic cylinder and piston, said piston beingconnected to actua'te said mechanism, a source of fluid pressure, avalve in said system to alternatively connect each end of said cylinderwith the pressure supply and exhaust the opposite end thereof, meanscontrolled by the movement of said mechanism for actuating said valve,independent manually operable valves in said system for adjustablycontrolling the rate of flow of the exhausting fluid from the ends ofsaid cylinder to thereby independently control the rate of movement ofthe workholder in each of its reciprocating directions, a pressurerelease valve in such system operable consequent upon a predeterminednumber of reeiprocations of said mechanism to release the pressuresupply in said system and means for manually determining the number ofreciprocations to be made before the release valve becomes active.

5. A polishing apparatus comprising a pair of polishing rolls, anoperating member, a workholder, a pair of parallel links pivotallyinterconnected between said member and said work holder, a fluidpressure system for moving the operating member to cause the movement ofthe workholder to and from the bite of said rolls to move a workpiecebetween the coacting faces of the rolls, independent motors for drivingsaid rolls, means for swinging the parallel links about their pivotalconnection with the operating member to move the workholder in adirection substantially parallel to the axes of the rolls, whereby avibratory movement is imparted of the workholder in a directiontransverse to the direction of reciprocation of the workholder, and anindependent motor for actuating said last-named means.

7. In a polishing machine, a frame having a table, a pair of coactingpolishing rolls suspended beneath the table with their axes in asubstantially horizontal plane, a guide mounted on said table, a slideon said guide, a hydraulic ram connected to said slide to reciprocatethe slide in a vertical direction on the column, a workholder connectedto said slide whereby the reciprocation of the slide may pass the workbetween the bite of said rolls, means to align the rolls with theworkholder, means to move the workholder in a direction substantiallyparallel with the aXes of the rolls, a fluid pressure system forreciprocating said slide, said system including a pressure releasevalve, means actuated by the movement of said slide to move the releasevalve to a pressure releasing position consequentfupon a predeterminednumber of passes of said work between the polishing rolls, and means insaid system to control the rate of flow of fluid to thereby control therate of speed of said reciprocating movement.

8. In a polishing machine, a frame having a table, a pair of coactingpolishing rolls suspended beneath the table with their axes in asubstantially horizontal plane, a vertically extending column mounted onsaid table, a slide on said column, a hydraulic ram connected toreciprocate the slide in a vertical direction on the column, a pair oflinks connected to said slide, a wcrkholder pivotally connected to thelower ends of said links, whereby the reciprocation of 'the slide maypass the work between the bite of said rolls, means acting on one ofsaid links to vibrate the workholder in a direction substantiallyparallel with the axes of the rolls, a fluid pressure system forreciprocating said slide and including a pressure release valve,mechanism actuated by the movement of said slide and coacting with saidrelease valve to move the release valve to -a pressure releasingposition consequent upon a predetermined number of passes of said workbetween the polishing rolls, means in said system to control' the flowof fluid to thereby control the rate of speed of such rolls of saidreciprocating movement, and a pair of motors drivingly connected torespective rolls to drive the rolls.

9. In a polishing mechanism, a pair of polishing rolls, a workholderarranged and adapted to feed work into the bite of said polishing rolls,a lconstant speed electric motor for each roll, said motors beingsubstantially identical electrically, a manually operable variable speeddriving unit interposed between each motor and its respective roll, anelectric circuit for controlling the operation of each of said motors,each circuit including an ammeter, a starting switch for initiating saidcircuits, means associated with said starting switch to cause saidammeters to be shunted out of the motor circuits, a second switchconnected to release said shunt and render both ammeters active forcausing both motors to cease to function in the event of failure of theelectrical circuit for either motor.

10. The method of maintaining identical surface speeds of a pair ofcoacting polishing rolls of a polishing apparatus, each of which rollsis rotated by an independent electric motor, said motors beingsubstantially identical and operated at substantially the same constantspeeds comprising measuring the electrical load on each motor andvarying the speed of the rolls to maintain substantially identical flowof current through the motors.

11. The method of maintaining identical surface speeds of a pair ofcoacting polishing rolls in a polishing machine each of which rolls isrotated by an independent electric motor which is connected to the rollsby a variable speed power transmission device, said motors beingsubstantially identical and operated at substantially the same constantspeeds comprising measuring ,the

electrical load on each motor and varying the speed ratio of the powertransmission device of one of lthe rolls until the current flow throughboth motors is identical.

HERBERT T. NICHOLAS.

REFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATENTS Number Name Date `77,646 Norton May 5, 1865534,394 Johnston Feb. 19, 1895 1,168,858 Coleman Jan. 18, 1916 2,095,501Johnson Oct. l2, 1937 2,114,349 Johnson Apr. 19, 1938 2,171,799 KlineSept. 5, 1939 2,338,599 Ridgway Jan. 4, 1944

